1. Field of the Invention
The present invention relates to two-port isolators and communication apparatuses, and more specifically, to a two-port isolator and a communication apparatus used in the microwave band.
2. Description of the Related Art
In general, isolators permit signals to be transmitted only in the transmission direction while preventing transmission in the opposite direction, and are used in transmission circuit sections of mobile communication apparatuses, such as automobile telephones and portable telephones.
In the related art, Japanese Unexamined Patent Application Publication No. 2002-26615 (Patent Document 1) discloses a two-port isolator in which an assembly that is formed by winding center electrodes made of insulation-coated wires around a substantially square-shaped ferrite is disposed vertically upright on a laminated substrate. The laminated substrate includes circuit devices (capacitors, resistors, and inductors) for a matching circuit, and terminal electrodes defined thereon.
Japanese Unexamined Patent Application Publication No. 2004-15430 (Patent Document 2) discloses a two-port isolator which includes a center-electrode assembly having center electrodes defined by electrode films that are mounted on a ferrite, the two-port isolator being mounted on a laminated substrate. The laminated substrate includes circuit devices for a matching circuit, and terminal electrodes defined thereon.
However, in the isolator disclosed in Patent Document 1, the ferrite having the center electrodes mounted thereon is substantially square-shaped, and is disposed vertically upright on the laminated substrate, which makes it difficult to provide an isolator having a low-profile design. In the isolator disclosed in Patent Document 2, the ferrite and a permanent magnet are vertically laminated on the laminated substrate, such that the permanent magnet requires a certain thickness, thus again making it difficult to provide an isolator having a low-profile design.
Although there is a demand for a low-insertion-loss isolator, the square-shaped or round-shaped ferrite disclosed in Patent Documents 1 and 2 makes it difficult to reduce the insertion loss in a wide band.